Variable pitch fan



' April 1964 D. M. LIEBHART 3,130,677

VARIABLE PITCH FAN Filed Jan. 29, 1962 INVENTOR. DORSE Y M. LIEBHART AIIORNEY United States Patent 3,130,677 VARIABLE PITCH FAN Dorsey M. Liehhart, 5224 NE. 42nd Ave., Portland 18, Greg. Filed Jan. 29, 1962, Ser. No. 169,503 2 Claims. (Cl. 103-37) This invention relates to a variable pitch fan and has particular reference to a fan used for driving a pump in an aircraft spray system.

In spraying crops and forests and the like from an airplane, tubular spray booms equipped with nozzles are mounted on the wings. The pressure employed in the spray system depends upon the kind of spray material and the amount of material to be applied per acre. The

. great variation in these factors for different crops and different kinds of pests makes it desirable to be able to change the speed of the pump. Such pumps are usually driven, however, by a fan exposed to the slip stream adjacent to the body of the airplane whereby the fan rotates at a fairly constant speed. Conventional pitch changing mechanisms used on other fans and propellers are too complicated and expensive for the present purpose.

Objects of the invention are, therefore, to provide convenient means for changing the pitch of the blades of a small wind-driven fan in order to change the speed of the fan, to provide a fan having removable blades so that the number of blades may be varied, and to provide a rugged and durable fan of the type described which is relatively simple and inexpensive to manufacture.

The present fan construction has provision for six blades. Each blade is supported by a cylindrical shank which is clamped in semi-cylindrical recesses in two mating plates. A radial pin on each shank engages a rotatable pitch change plate. When t-he clamping pressure on the two clamp plates is released, the pitch change plate may be rotated slightly which, in turn, rotates all the blades to vary the pitch as desired and thereby change the speed of the fan. When the clamping plates are again secured, the blade pitch is fixed against accidental variation.

The construction is such that alternate blades may be removed to provide a three-blade fan or, if desired, four of the blades may be removed to provide a two-blade fan. In these ways the characteristics of the fan may be altered so that a single fan will meet the widely varying requirements of the pump.

The invention will be better understood and additional objects and advantages will become apparent from the following description of the preferred embodiment illustrated on the accompanying drawing. Various changes may be made, however, in the details of construction and arrangement of parts and all such modifications within the scope of the appended claims are included in the invention.

In the drawing:

FIGURE 1 is a perspective view of a fan and pump combination embodying the principles of the invention;

FIGURE 2 is an exploded view of the fan; and

FIGURE 3 is an enlarged view of the pitch change plate shown in FIGURE 2.

In FIGURE 1 the fan is mounted on the shaft of pump 11. The rear side of the pump housing is equipped with suitable brackets, not shown, for mounting the pump and fan on an airplane or helicopter, so that the fan will be rotated by its forward movement through the air.

Referring now to FIGURE 2, the pump has a shaft 12 and a stationary front end structure 13 equipped with a plurality of tapped holes 14 to receive screws through apertured ears 15 on a brake housing 16. Brake hous- "ice ing 16 contains conventional internal expanding brake shoes engageable with the brake drum 17 which rotates with the shaft 12. The brake mechanism is equipped with a lever, not shown, for actuating the shoes against the drum to stop the pump when desired.

A fan body plate 20 has a hub 21 which is keyed and secured to the shaft 12. This hub projects rearwardly into a central opening 19 in the brake drum and is disposed between the arcuate brake shoes therein. Three long bolts 22 having heads within the brake drum pass through bosses 23 in body plate 20 for mounting the brake drum on the body plate. Body plate 20 is provided with six radially directed semi-cylindrical recesses 25 to receive cylindrical shank portions 26 on the blades 27. Deeper recesses 28 accommodate the shouldered portions 29 of the shanks which carry pins 30 projecting radially from the shanks.

A saddle plate 31 is constructed similarly to body plate 20 to mate therewith except that the saddle plate does not have a hub. Thus, the saddle plate has six semi cylindrical recesses 25a to register with the recesses 25 in the body plate and form cylindrical bores surrounding the cylindrical blade shanks 26. Pins 30 project forward through openings 32 in the saddle plate. Saddle plate 31 is equipped with three apertured bosses 33 to receive the three bolts 22. The forward ends of these bolts carry nuts and Washers 34 which bear against the bosses 33 to clamp brake drum 17 against the rear face of body plate 20 and clamp saddle plate 31 against the frontface'of' the body plate. The bores 25 and 25a are dimensioned to grip the blade shanks 26 and clamp them securely when the nuts 34 are tightened.

A triangular pitch plate 35 fits against the front face of the saddle plate. Pitch plate 35 has three fiat sides 36 to clear the bosses 33 and bolts 22, as shown in FIGURE 3, and three apex corners 37 provided with arcuate slots 38. Between each flat side 36 and a corner portion 37 is a notch 39 to engage one of the pins 30. The pitch plate is mounted on three bolts 4% which have heads on their rear ends inside the brake drum 17 and pass through three apertured bosses 41 in body plate 20 and thence through three circular holes 42 in saddle plate 31. The forward ends of bolts 41) pass through arcuate slots 38 to support pitch plate 35 for limited rotation about the axis of shaft 12.

When the pitch plate is rotated, its notches 39 shift pins 30 to rotate all the blades 27 simultaneously about the axes of their shanks 26 to vary the pitch of the blades through a range of 15 to 40. The pitch plate 35 is clamped in adjusted position by nuts and washers 43. As shown in FIGURE 2, one of the bolts 22 carries a pointer 4-5 which indicates the blade angle on a scale 46 on the pitch plate. A streamlined spinner cup 50 protects the adjusting mechanism and directs the air into the spiral curved blades for the greatest efficiency of the fan. The spinner cap is secured by a screw 51 which passes through a central hole 53 in the pitch plate and engages a tapped hole 52 in the end of shaft 12.

In changing the pitch it is most convenient to rotate plate 35 by grasping any two opposite blades 27 and rotating them in opposite directions on the common axis of their shanks 26. This will rotate plate 35 to the desired pitch angle as indicated on scale 46.

When it is desired to adjust the pitch of blades 27, screw 51 and spinner cap 50 are first removed. Then the three nuts 34 and the three nuts 43 are loosened. This permits pitch plate 35 to be rotated to the desired blade pitch as indicated on scale 46. If it is desired to remove some of the blades, the nuts 34 and 43 are loosened sufficiently to permit saddle plate 31 to move forward from body plate 20 far enough to allow shouldered portions 29 to be withdrawn out of the bores 25, 25a. Every other blade may be removed to provide a threebladed fan or four of the blades may be removed to provide a two-bladed fan. When the nuts 34 and 43 are tightened, both the pitch plate 35 and the shanks 26 are clamped securely in adjusted position. The shouldered portions 29 on the blade shanks provide positive locks in the recesses 28 to prevent withdrawal of the blades by centrifugal force.

Thus, the blades are both secured and made adjustable by the three parts 20, 31 and 35 which may be made as inexpensive die castings. The blades and their shanks may be made entirely of a strong and durable plastic except for the pins 30 which are preferably made of steel and included as integral parts of the blade shanks during the molding operation. This provides an economical form of construction which is very durable and fully satisfies the variable speed requirements of the pump for crop spraying purposes.

Having now described my invention and in what manner the same may be used, what I claim as new and desire to protect by Letters Patent is:

l. A variable pitch fan for driving a rotary mechanism comprising a body plate having a hub for a shaft, a plurality of semi-cylindrical recesses in said plate radial to said hub, a plurality of bolts parallel with the axis of said hub passing through said body plate, a saddle plate mounted on said bolts and having semi-cylindrical recesses mating with said first recesses to form cylindrical bores, fan blades having cylindrical shanks in said bores, pins on said shanks radial to said shanks, said saddle plate having openings for said pins, a second plurality of bolts parallel with the axis of said hub and passing through said body and saddle plates, a rotatable pitch plate adjacent said saddle plate having arcuate slots for mounting the pitch plate for limited rotation on said last bolts, said pitch plate having notches in its edge portions engaging the pins of all of said blade shanks and arranged to change the pitch of all the blades in unison, nuts on said first plurality of bolts for clamping said body and saddle plates against said blade shanks, and nuts on said second plurality of bolts to clamp all of said plates together and prevent rotation of said pitch plate relative to said body and saddle plates..,

2. A spray pump for aircraft comprising a pump having a housing and an impeller shaft, a brake mechanism mounted on said pump housing, a body plate having a hub secured on said shaft, a plurality of semi-cylindrical recesses in said plate radial to said hub, a brake drum surrounding said brake mechanism, a plurality of bolts parallel with said shaft passing through said brake drum and said body plate for mounting the brake drum on said body plate, a saddle plate mounted on said bolts and having semi-cylindrical recesses mating with said first recesses to form cylindrical bores, fan blades having cylindrical shanks in said bores, pins on said shanks radial to said shanks, said saddle plate having openings for said pins, a second plurality of bolts parallel with said shaft passing through said brake drum and said body and saddle plates, a pitch plate adjacent said saddle plate having arcuate slots for mounting the pitch plate for limited rotation on said last bolts, said pitch plate having notches in its edge portions engaging the pins of all of said blade shanks and arranged to change the pitch of all the blades in unison, nuts on said first plurality of bolts for securing said brake drum to said body plate and for clamping said body and saddle plates against said blade shanks, and nuts on said second plurality of bolts to clamp said brake drum and all of said plates together and prevent rotation of said pitch plate relative to said body and saddle plates.

References Cited in the file of this patent UNITED STATES PATENTS 546,630 Tuerk Sept. 17, 1895 1,455,153 Smith May 15, 1923 2,350,383 Bebinger June 6, 1944 2,458,197 Pierce Jan. 4, 1949 2,517,714 Roesch Aug. 8, 1950 2,612,961 Kapsenberg Oct. 7, 1952 2,909,229 Cross et al. Oct. 20, 1959 2,924,040 White et a1. Feb. 9, 1960 

1. A VARIABLE PITCH FAN FOR DRIVING A ROTARY MECHANISM COMPRISING A BODY PLATE HAVING A HUB FOR A SHAFT, A PLURALITY OF SEMI-CYLINDRICAL RECESSES IN SAID PLATE RADIAL TO SAID HUB, A PLURALITY OF BOLTS PARALLEL WITH THE AXIS OF SAID HUB PASSING THROUGH SAID BODY PLATE, A SADDLE PLATE MOUNTED ON SAID BOLTS AND HAVING SEMI-CYLINDRICAL RECESSES MATING WITH SAID FIRST RECESSES TO FORM CYLINDRICAL BORES, FAN BLADES HAVING CYLINDRICAL SHANKS IN SAID BORES, PINS ON SAID SHANKS RADIAL TO SAID SHANKS, SAID SADDLE PLATE HAVING OPENINGS FOR SAID PINS, A SECOND PLURALITY OF BOLTS PARALLEL WITH THE AXIS OF SAID HUB AND PASSING THROUGH SAID BODY AND SADDLE PLATES, A ROTATABLE PITCH PLATE ADJACENT SAID SADDLE PLATE HAVING ARCUATE SLOTS FOR MOUNTING THE PITCH PLATE FOR LIMITED ROTATION ON SAID LAST BOLTS, SAID PITCH PLATE HAVING NOTCHES IN ITS EDGE PORTIONS ENGAGING THE PINS OF ALL OF SAID BLADE SHANKS AND ARRANGED TO CHANGE THE PITCH OF ALL THE BLADES IN UNISON, NUTS ON SAID FIRST PLURALITY OF BOLTS FOR CLAMPING SAID BODY AND SADDLE PLATES AGAINST SAID BLADE SHANKS, AND NUTS ON SAID SECOND PLURALITY OF BOLTS TO CLAMP ALL OF SAID PLATES TOGETHER AND PREVENT ROTATION OF SAID PITCH PLATE RELATIVE TO SAID BODY AND SADDLE PLATES. 